This power point presentation is on COVALENT BONDING and INTERMOLECULAR FORCES

1. This power point presentation is on COVALENT BONDING and INTERMOLECULAR FORCES It also covers metallic bonding. Please take notes as you go, but there is some good news at the end for you.

2. COVALENT BONDING This involves the sharing of electrons by 2 or more atoms. The electrons are shared. They are not transferred to the anion from a cation as with ionic bonds. EXAMPLES INCLUDE THE BONDS BETWEEN: H2 F2 Br2 Cl2 HCl H2O

3. these are NOT ionic bonds Ionic bonds ONLY happen with cations and anions that are metals and non-metals. All compounds that you just saw are made with non-metals only.

4. In a chlorine molecule, each of the atoms shares one pair of electrons circled in GREEN, making the covalent bond. Since it’s just one pair being shared, this is a SINGLE COVALENT BOND. Each of the chlorine atoms also has three pairs each of UNSHARED ELECTRONS. THEY BOTH GET AN OCTET BY SHARING.

5. unshared electrons When electrons are written into the Lewis diagrams, they are usually paired. The electrons prefer pairs. When they share themselves with other atoms, one electron from each atom connects together, making a SINGLE BOND. Electrons not involved in bonding are mostly paired away from the bond. They are the “unshared” electrons. If they connect 2 or 3 pairs at a time, they make DOUBLE or TRIPLE BONDS.

6. Water has two hydrogen atoms bonded to one oxygen atom. It has 2 single covalent bonds. The oxygen has 2 pairs of unshared electrons as well. Oxygen gets the octet. 2 pairs of unshared electrons on oxygen.

7. ammonia NH3 has three single covalent bonds, and nitrogen has one unpaired set of electrons. N gets the octet. Nitrogen’s electrons are RED and the Hydrogen electrons are inBLUE. there are 2 red, unshared electrons of nitrogen down here

8. methane Methane has FOUR single covalent bonds, and that leaves the carbon atom without any unshared pairs of electrons. But that’s okay, as long as the electrons are either paired up or being shared, they are well taken care of and the molecule is okay.

9. When 2 oxygen atoms combine to form a molecule, each keeps two pairs of unshared electrons, but shares two pairs (in the middle) with each other. That is a DOUBLE COVALENT BOND

10. This is a rough diagram but you get the point here… Diatomic Nitrogen makes a TRIPLE COVALENT BOND and each atom keeps one pair of UNSHARED ELECTRONS.

11. POLAR vs. IONIC Polar bonds happen when ever atoms with large electro-negativity differences connect. The electrons are not shared evenly, they get taken by the anion. Ionic bonds happen when polar bonds are made between a non-metal and a metal. Ionic bonds are always polar. Polar bonds are not always ionic.

12. This is the SULFITE (–2) ion By gaining 2 electrons all together, sulfur as well as the three oxygen atoms end up with a complete octet. This poly atomic ion acts as a negative two unit. Sometimes in these Lewis dot diagrams, we use dots as well as X’s. The X’s just indicate electrons from the “other” atoms or ions. If we used just dots you might get confused as to where all those electrons came from or belong.

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14. bond polarity Bonds can be polar or non-polar. If a bond is non-polar, that means that there is not a taking of electrons, making for a positive side and a negative side of the bond. If a bond is polar, that means that the electrons are not shared equally, making one side of the bond more negative (where the electrons end up) and the other side more positive (where the electrons were).

15. HCl is a polar covalent bond. Your first guess might be that it’s ionic, but it’s not. Ionic bonds are ONLY between metals and non-metals. Hydrogen and chlorine are bothnon-metals. Water also has polar covalent bonds between the H and the O. The oxygen is very attracted to the electrons of hydrogen, so they take them away, making an octet. The hydrogen side of the molecule ends up more positive while the oxygen side is more negative.

16. MOLECULAR POLARITY a molecule can also be polar, if the electrons are moved about by polar bonds giving the WHOLE MOLECULE a positive and a negative side. The opposite sides of polarity are called dipoles, which means 2 poles, the positive and the negative side. The oxygen side is negative since it takes the electrons, the hydrogen side is more positive because it lost the electrons.

17. Molecules are polar when they do not have radial symmetry. If molecules have radial symmetry they are non polar. Methane has radial symmetry, it’s nonpolar even though each of the four bonds inside it are polar. Ammonia does not have radial symmetry,it’s a polar molecule.

18. polar compounds are formed when 2 atoms with different electro-negativities form a covalent bond. The atoms DO NOT SHARE electrons equally. The electrons are more strongly attracted to the MOST electronegative atom. (see table S for E-N values)

19. Sort of like, but not really like these love birds, molecules can also be attracted to each other. Different forces make them stick together. Love is not one of the forces. Neither is nesting instinct. But it really was a nice picture to use.

20. WEAK FORCES … there are 3 kinds of weak forces that keep some molecules sticking together. They are weak & also knownas van der Waal’s forces, named after a chemist whose name was not Arbuiso.

21. The first weak force holding molecules together are called dipole forces. They are due to the permanent dipole (positive and negative) attractions between different sides of molecules to each other. The force is ELECTROSTATIC, but much weaker than the electrostatic forces holding ionic bonds together. Phosphorous tri chloride has good permanent dipole forces. Chlorine is mostly negative, so they attract to the neighboring phosphorous atoms in other PCl3 molecules.

22. Dr. Van der Waal, the weak force chemist. The other weak force is called the electron dispersion force, which is due to the movement of molecules and to the number of electrons around. They create temporary but real attractions between molecules. The more electrons, the more dispersion force. For example, both F and Cl are gases at STP because there are not too many electrons in those atoms. Br makes a liquid at STP and there are lots more electrons in bromine compared to the first 2 atoms. Iodine has the most electrons of all in group 17 and it’s a solid at STP. More electrons make for more forces (all the while temperature and pressure were constant).

23. dispersion forces When you have a lot of electrons and they are all buzzing around quickly from time to time a temporary condition can be created where there are more electrons over there than here. This creates a temporary but real electrostatic force of attraction between the (+) and the (-) zones created. The more electrons you have (Iodine has lots more than fluorine for example) the more opportunity for this temporary condition to exist. It’s weak but real and in group 17 at STP the results make for some gases, a liquid and a solid at constant STP.

24. hydrogen bonds … is the other force keeping molecules attracted to each other always includes hydrogen. These are the exact same thing as the first one, permanent dipole attractions, but they are stronger. When hydrogen bonds to certain highly electro-negative atoms such as oxygen, nitrogen or fluorine, the bonds are very polar. This leaves the hydrogen rather positive, wishing for some negativity in the form of electrons. Since it can’t pull its electron back from these atoms, it actually is attracted to the UNSHARED PAIRS of electrons from other nearby molecules.

25. The + signs in blue are the hydrogen atoms without electrons. See how they can be attracted to the blue UNSHARED PAIRS of electrons of a nearby water molecule? That is hydrogen bonding. the hydrogen bond is only about 5% the strength of a covalent bond, but much stronger than a dipole weak bond

26. The End